The papillomaviruses are associated with naturally occurring human carcinomas in a variety of species, including man. HPVs 5 and 8 have been associated with cutaneous carcinomas in patients with epidermodysplasia verruciformis. HPVs 16 and 18 have been associated with carcinoma in situ as well as invasive carcinomas of the cervix in man. In addition, HPV-18 has been reported to be present within Hela cell DNA. Papillomaviruses in general cause benign tumors and there a number of animal systems where progression of the benign lesion into a carcinoma occurs. In general, this occurs after a period of time and often in the association with a second co-carcinogenic agents. The mechanism of this carcinogenic progression is unknown.